As feature sizes of integrated-circuit devices continue to decrease, it becomes increasingly difficult to design well-behaved devices. The fabrication is also becoming increasingly difficult and expensive. In addition, the number of electrons either accessed or utilized within a device is decreasing, which produces increased statistical fluctuations in the electrical properties. In the limit, device operation depends on a single electron, and traditional device concepts must change.
Molecular electronics has the potential to augment or even replace conventional devices with electronic elements, can be altered by externally applied voltages, and has the potential to scale from micron-size dimensions to nanometer-scale dimensions with little change in the device concept. The molecular switching elements can be formed by solution techniques; see, e.g., C. P. Collier et al, “Electronically Configurable Molecular-Based Logic Gates”, Science, Vol. 285, pp. 391-394 (16 Jul. 1999) (“Collier I”) and C. P. Collier et al, “A [2]Catenane-Based Solid State Electronically Reconfigurable Switch”, Science, Vol. 289, pp. 1172-1175 (18 Aug. 2000) (“Collier II”). The self-assembled switching elements may be integrated on top of a semiconductor integrated circuit so that they can be driven by conventional semiconductor electronics in the underlying substrate. To address the switching elements, interconnections or wires are used.
For nanoscale electronic circuits, it is necessary to invent new materials with the functions envisioned for them and new processes to fabricate them. Nanoscale molecules with special functions can be used as basic elements for nanoscale computing and memory applications.
While self-assembled techniques may be employed and while redox reaction-based molecules may be used, such as rotaxanes, pseudorotaxanes, and catenanes, other techniques for assembling the devices and other molecular systems may alternatively be employed. An example of such other techniques comprises lithographic techniques adapted to feature sizes in the micrometer-size range, as well as feature sizes in the nanometer-size range. An example of other molecular systems involves electric-field-induced band gap changes, such as disclosed and claimed in patent application Ser. No. 09/823,195, filed Mar. 29, 2001, which is incorporated herein by reference. While prior references have employed the term “band gap”, this term more precisely is used for semiconductors. The corresponding term with regard to molecules is “HOMO-LUMO gap” (highest occupied molecular orbital—lowest unoccupied molecular orbital), and that is the term that will be used throughout.
Examples of molecules used in the electric-field-induced HOMO-LUMO gap change approach include molecules that evidence:                (1) molecular conformation change or an isomerization;        (2) change of extended conjugation via chemical bonding change to change the HOMO-LUMO gap; or        (3) molecular folding or stretching.        
Changing of extended conjugation via chemical bonding change to change the HOMO-LUMO gap may be accomplished in one of the following ways:                (a) charge separation or recombination accompanied by increasing or decreasing HOMO-LUMO localization; or        (b) change of extended conjugation via charge separation or recombination and n-bond breaking or formation.        
Molecular electronic devices hold promise for future electronic and computational devices. Examples of such molecular electronic devices include, but are not limited to, crossed wires, nanoporous surfaces, and tip addressable circuitry which forms switches, diodes, resistors, transducers, transistors, and other active components. For instance, a crossed wire switch may comprise two wires, or two electrodes, for example, with a molecular switching species between the two electrodes. Thin single or multiple molecular layers can be formed, for example, by Langmuir-Blodgett (LB) techniques or self-assembled monolayer (SAM) on a specific site. Well-controlled properties, such as roughness and hydrophilicity of the underlying surface are needed to allow optimal LB film formation.
Prior work in the field of molecular electronics has utilized electrodes of gold (Reed et al, Science, Vol. 278, pp. 252-254 (1997); Chen et al, Science, Vol. 286, pp. 1550-1551 (1999)), aluminum (Collier I, supra), and polysilicon (Collier II, supra).
Gold has a low melting point, low bulk modulus, and high diffusivity, making it less stable with respect to external stress and incompatible with a standard CMOS process, although it has the advantages of no oxide and the chemical stability of a noble metal. Aluminum forms a poorly controlled native oxide that acts as a natural barrier to electronic transport. Polysilicon is a semiconductor with associated semiconductor properties, giving it lower conductivity than a metal and an oxide barrier to transport. Polysilicon electrode molecular devices have been fabricated and shown to display switching (Collier et al, supra).
Platinum is difficult to maintain in a stable form. During the interval following Pt deposition and preceding the next processing step, an “environmental” film (carbon, etc.) will form on the surface. This is a particular issue when the active molecular layer may be on the order of 20 Å thick, which, for reference, is the same magnitude as a native silicon oxide. Working with a just-deposited-film (perhaps the “cleanest” way) is difficult and impractical. Even a “just-deposited” blanket film will require time to move to the next process, which will not be in ultrahigh vacuum (UHV). Until alternate means of forming patterned contacts are readily realizable, lithography is presently the most likely technology to use. Shadow masks avoid lithographic process, but are dimensionally limited (to large micron-sized dimensions, sparsely placed) Even nanoimprinting exposes surfaces to organic chemicals that are potentially incompatible with the use of organic active layers. Therefore, the most practical way to fabricate electrodes incorporating molecules is to pattern the electrode with a flexible geometry in a cost-efficient, time efficient, flexible geometry way and then clean the organics from the surface before subsequent processing
Thus, a method for preparing platinum, and other conductive electrodes, that avoid most, if not all, of the foregoing problems is required for use with molecular films for forming molecular electronic devices. In addition, it would be an advantage to tailor the surface to desired device specifications for use even if lithographic steps are not employed.